Such electrical devices, particularly motors, must have a protection against explosions for various environments so as to protect persons and objects against damage. According to the DIN standard EN 50014, different protection classes are prescribed for different environments, for example, the low protection class ex-p and the adjoining higher protection class ex-d. The sensor may be used for various purposes, for example, for position information for the motor as such or for the rotor, for regulating the speed of the motor, etc.
The protection class ex-p prescribes that the motor protection housing and the sensor protection housing have to be designed to be only overpressure-resistant, requiring the implementation of suitable purging measures. For this purpose, the overpressure-resistant protective housings must be provided with purge openings to which for the motor protection housing as well as for the sensor protection housing in each case a separate monitored purge circuit having a monitoring device and a purge device is connected.
The protection class ex-d prescribes that the motor protection housing and the sensor protection housing must be designed to be pressure-resistant, the sensor itself having to be designed to be explosion-proof. The protective housings must pressure-resistant to such a degree that, if an ignitable gas mixture explodes in these protective housings, they withstand the explosion in the interior without igniting an ignitable gas mixture outside these protective housings. Purge circuits are not required in this case.
In protection class ex-p two purge circuits having the appropriate devices and an explosion-protected sensor are thus required, whereby substantial costs for protection are incurred. In protection class ex-d, high-quality protective housings and also an explosion-protected sensor are required such that substantial costs also arise for protection.
An objective of the present invention is to provide a protective device, in which a reliable explosion protection is obtained at the lowest possible expense.